1. Field of the Invention
The present invention is in the field or rotary seals for low pressure applications, and particularly for rotary seals for vertical shafts which pass through a casing, such as a wall, of a mixing container, feed auger assembly or the like.
2. The Prior Art
In many applications it is necessary to isolate a shaft bearing or the like disposed below a casing or vessel from pulverulent material located within the casing so that increments of the material do not pass downwardly through the area surrounding the shaft and contaminate the bearings or drive motor.
The typical sealing system utilized for such purpose employs a waste or packing suitably impregnated with a lubricant, the packing being mounted in a gland surrounding the shaft and pressing against the shaft. The sealing effect of such an arrangement is, of course dependent upon and proportional to the force with which the packing is pressed against the shaft periphery.
Seal devices operating on such basis are disadvantageous on many counts. Specifically, if the packing is tightly compressed against the shaft to effect a tight seal, starting torque is extremely high, ranging up to six or seven times the running torque. Moreover, seals depending upon packing pressure against the shaft require frequent adjustment of the gland to compensate for wear in the packing material.
Additionally, in an environment where the packing material is free to contact the material being processed, e.g. grinding or mixing application, lubricant from the packing will contaminate the material being processed. Similarly, the processed material may be absorbed into the packing and accelerate wear of the shaft.
The typical packing gland of the type mentioned will require adjustment every one hundred to two hundred hours of use, and will require complete replacement of packing about ever three months.
Packing gland seals engender the additional drawback, that they are incapable of compensating for eccentricities or axial misalignments between the rotating shaft and fixed components.